This invention relates generally to motor vehicle steering columns and more particularly to such columns which include a temperature insensitive tunable collapse mechanism for energy management during collisions.
Collapsible steering columns have been provided on motor vehicles to reduce injury to operators during collisions. In virtually all such columns considerable effort has been directed to minimization of rotational lash between the telescoping components in order to provide a solid feel to the operator during steering maneuvers. Such efforts commonly employ inserts, either formed in place or added during assembly, of polymeric materials which provide damping of lash between the column components. Over time, however, due to repeated alternating stress on the inserts under varying temperature conditions, the inserts become loose and sensible lash is introduced to the steering column. This either requires replacement of column components or development of operator tolerance for a feel of loose steering.
In addition, the collapse of the column must provide sufficient resistance during collisions to provide controlled absorption of the energy generated by the possible impact of the operator with the steering wheel. For this purpose, many different energy absorbing mechanisms of varying merit have been developed including springs, levers, frangible or deformable tubes and shafts, friction couplings, and tearable strips. These must fit within the space provided between the steering wheel in the passenger compartment and the steering gear box in the engine compartment. The more complex the mechanism for energy absorption, the more space it requires. Thus it is often required to locate the collapsible portion of the steering column in the engine compartment. This creates a life-limiting exposure of polymeric components of the column to temperature extremes exceeding 250 degrees Fahrenheit, and it results in reduced reliability of the energy absorption behavior and in reduced solidity of feel of the steering column.
The foregoing illustrates limitations known to exist in present collapsible energy absorbing steering columns. Thus, it would clearly be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.